Good post.
People need to appreciate that prosecutors cannot layout a storyline to the jury that supports both murder one and aggravated manslaughter. Moreover, if they do not lay out a storyline in their opening statement, that will tell me that they are almost certainly but whistling into the wind.
Prosecutors do provide opening statements that include the bases for both manslaughter and first degree murder. Here's a simplistic version of one for this case:
"Ladies and Gentlemen of the jury, you will hear testimony that a little girl named Caylee died, that her mother was the last person seen on this earth with her, and that her body was found discarded in the woods in a trash bag. It will be up to you to determine whether Casey Anthony planned in advance to kill her child, or whether the death of her child was an accident. ..."